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Emerging pathogens threaten aquaculture industries worldwide. There is urgency to become better prepared and meet these challenges, as aquaculture is growing rapidly and will contribute increasingly to food security. There are important Pacific oyster production areas today as yet unchallenged by emergent OsHV-1 microvariants, notably in the Americas, and to these areas the viruses are an immediate threat.The ICES Workshop on Emerging Mollusc Pathogens addressed fundamental questions regarding capabilities (expertise, infrastructure) and communication (among the pathology community, regulation, and industry). We sought to identify areas warranting investment and support to manage emerging diseases in shellfish aquaculture industries, and to provide justification for resources to be directed to these areas for more effective management of shellfish health. Thirty-six priorities were identified spanning four areas: i) improving communication and frameworks; ii) essential infrastructure and expertise; iii) key research priorities; and iv) the central role of husbandry in shellfish aquaculture health management. Improving communication in every regard was recognized as the greatest need. Better coordinating efforts, improving data sharing, and improving trust on the part of industry to create buy-in and improve reporting were among identified priorities. Regulatory frameworks were recognized as needing to be flexible, given the often urgent need to act with incomplete information when a disease emerges.For essential infrastructure and expertise the workshop emphasized the continued importance of traditional fields such as pathology, bacteriology and virology, which remain foundational to aquaculture health management. Maintaining laboratory capacity is critical, in distribution as well as technologically: there is value in maintaining not just national or pan-national laboratories but provincial governmental and academic labs too, which can be more intimately engaged with local producers, and familiar with local environments. Disease challenge models and facilities were additionally identified as essential for testing hypotheses, as was expertise in epidemiology, which is sharply limited for marine systems.Discussion of key research priorities highlighted the value of long-term studies for understanding infection patterns; for appreciating dynamics like resistance and tolerance evolution versus virulence evolution; and for understanding effects of changing environments. The importance of improving ecological and evolutionary perspective in general was emphasized, as was the need to develop strategies for monitoring the diversity of potential pathogens. Establishment of mol-luscan cell lines for viral work would be a particularly valuable tool.Aquatic animal husbandry offers myriad opportunities to control pathogens. Understanding inter-sections of disease with aquaculture production for different host-pathogen systems requires continued research investment. Focused investment is also required to pursue strategies emerging from this research, including disease resistance breeding. Tighter collaboration among practical aquaculture scientists and breeders and pathologists should be promoted.Finally, funding was recognised as a continuing challenge. Priorities of donors and funding agencies do not always match commercial and health management priorities; basic surveillance is a key area difficult to support. Short funding timelines challenge our ability to address key questions and challenges, including breeding to control diseases. And there is little funding for truly trans-national, collaborative research. Managing diseases to support aquaculture growth is a global problem that demands science that is equally global, which requires the capacity to build broad international collaborations. It would be immensely beneficial for sustainable aquaculture development if trans-national research initiatives in aquatic animal health and other aquaculture related fields could be established to support innovation in this area in the future.

Bonamia ostreae has been associated with the decline of flat oyster Ostrea edulis populations in some European countries. This obligatory intracellular parasite persists and multiplies into hemocytes. Previous in vitro experiments showed that apoptosis is activated in hemocytes between 1 h and 4 h of contact with the parasite. The flat oyster uses the apoptosis pathway to defend against B. ostreae. However, the parasite might be also able to modulate this response in order to survive in its host. In order to investigate this hypothesis the apoptotic response of the host was evaluated using flow cytometry, transmission electron microscopy and by measuring the response of genes involved in the apoptotic pathway after 4 h. In parallel, the parasite response was investigated by measuring the expression of B. ostreae genes involved in different biological functions including cell cycle and cell death. Obtained results allow describing molecular apoptotic pathways in O. edulis and confirm that apoptosis is early activated in hemocytes after a contact with B. ostreae. Interestingly, at cellular and molecular levels this process appeared downregulated after 44 h of contact. Concurrently, parasite gene expression appeared reduced suggesting that the parasite could inhibit its own metabolism to escape the immune response.

Alignment of Mikrocytos small subunit ribosomal gene sequences obtained in the present study. (DOCX 197 kb)

Transmission electron microscopy of Mikrocytos veneroïdes n. sp. at different stages. (DOCX 1814 kb)

Parue en abstract dans Frontiers in Veterinary Science; Animal movements are one of the main ways to introduce and spread pathogens. In French oyster farming, many stakeholders and premises are heterogeneously divided over the country and a highly dynamic flow of oysters exists among them. In the context of animal disease surveillance and control, analysis of the animal movement’ network can provide useful information to build adapted surveillance strategies or to develop risk management. Movement network analysis has been widely used in terrestrial production, to evaluate the vulnerability of animal movement network to the spread of a specific disease.In France, since 2008, Pacific oyster spat (Crassostrea gigas) has been affected by massive mortality outbreaks associated with the detection of a newly reported variant of ostreid herpesvirus type 1 (OsHV-1). These mortality events have a direct economic impact causing considerable concern to oyster farmers. A previous epidemiological study has highlighted the potential role of oyster transfers in the spread of these outbreaks. However, neither mandatory database nor reliable data is publicly available concerning oyster transfers in France.In this context, a field study was carried out in the main oyster production area in France, Charente-Maritime bay, to map oyster movements and to characterize the corresponding network structure related to potential disease spread. Seventy-five oyster farmers were randomly selected in Charente-Maritime bay between July and September 2010, according to a stratified sampling design based on farm category regarding production type and location (i.e. spat producers, local farmers, beyond farmers, local farmer-senders, beyond farmer-senders). Data related to the farm characteristics and activities, routine rearing scheme and potential changes in husbandry practices were collected during a face-to-face interview of the oyster farmer, using a standardized questionnaire and a land register. Movement data were spatialized and analyzed using social network analysis.A 85.3% participation rate to the study was obtained. Results showed a seasonal variation of oyster transfers in all the sampling strata, with peaks of transfers in spring and autumn, and different geographical patterns of oyster transfers between strata. Growing sites were shared by farms belonging to different farm category which have different behaviour related to oyster movements in time. These results show heterogeneity of contacts between strata both in time and space. Network measures allowed identifying the growing sites having a high risk of becoming infected, of transmitting diseases to other sites or controlling the flow of oysters from one part of the network to another part. The growing sites at high risk of becoming infected could be targeted for surveillance activities (Figure 1). The growing sites at high risk of transmitting diseases to other sites could be the first ones where implementation of early or enhanced control measures (e.g. quarantine, depopulation) could be focused. The growing sites controlling the flow of oysters could be considered as key players in the initial spread of a disease. If these sites would be removed from the network by early movement restriction, this may contribute to contain the disease spread in a smaller part of the area, providing that the propagation by the marine currents and the effect of environmental factors are considered all together.As a conclusion, movement network analysis may provide valuable information to policy makers in preparedness (surveillance) and response (control) to an epidemic.

L’huitre plate, la seule huitre native des côtes européennes, est une espèce emblématique de Bretagne. Convoitée depuis l'Antiquité, sur-pêchée au 19ème siècle, fleuron de l'ostréiculture au 20ème, elle est désormais menacée de disparition à l'aube du 21ème. Sous l'impulsion de la commission OSPAR mais aussi dans un contexte grandissant de crise écologique et d'érosion de la biodiversité imposant une nécessaire conservation et/ou restauration de nos patrimoines naturels, une alliance européenne réunissant biologistes et gestionnaires a été créée en novembre 2017 à Berlin sous l'égide de l'Agence Allemande de Conservation de la Nature (BFN) avec un objectif commun: favoriser le retour de l'huitre plate sur les côtes européennes. Cette alliance pour la restauration de l'huitre plate (NORA) regroupe désormais plus d'une centaine de scientifiques et de gestionnaires, tous au chevet de cette espèce. En France, cette démarche est assurée nationalement par le programme FOREVER ("Flat Oyster Recovery"), démarré en 2018 et financé par le FEAMP pour sa première phase (2018-2020) focalisée en Bretagne. Le présent rapport dresse le bilan du projet. En trois ans, ce projet pionnier a permis : (1) de proposer un premier inventaire des dernières populations relictuelles d'huitres plates encore présentes en Bretagne, en fournissant un diagnostic de leur état écologique, parasitaire et génétique et en affinant la description de son habitat actuel. (2) d'étudier plus précisément les mécanismes écologiques impliqués dans la dynamique d'un banc d'huitres plates : abondance et dispersion larvaire, dynamique du recrutement, facteurs environnementaux, effet de la prédation, impact des maladies parasitaires. L'ensemble de ces processus est étudié à la fois en rade de Brest et en baie de Quiberon. (3) d'initier une démarche unique en France et proposer une méthode adaptée permettant la conservation et la restauration écologique des derniers bancs. Cette démarche inclue des opérations de communication et de sensibilisation actives associées à des actions pilotes concrètes et facilement transférables de restauration écologique : enrichissement coquillier, semis de naissain et développement de récifs artificiels adaptés à l'espèce. Ce rapport apporte aussi de nombreux nouveaux éléments de gestion, utiles aux professionnels de l'ostréiculture, de la pêche, mais aussi aux gestionnaires de l'environnement, notamment aux animateurs du réseau des sites Natura 2000, à l'Office Français de la Biodiversité ainsi qu'à différentes associations impliquées. A titre d'exemple, ci-joint quelques résultats marquants : Pour la profession ostréicole, la meilleure compréhension du recrutement de l'espèce ouvre les voies pour assurer un captage "régulier" pour les années à venir. Les cartes de dispersion expliquent la distribution spatiale du recrutement dans les deux seuls sites de captage français. Les tendances temporelles démontrent l'importance de gérer les populations sauvages, seul moyen d'assurer un captage lorsque des étés frais moins favorables à la reproduction. Le seuil des 18°C/19°C constitue une température critique des masses d'eau en deçà de laquelle le recrutement se fait mal, surtout quand les stocks sont faibles. Pour le secteur de la pêche professionnel (mais aussi récréative), les résultats montrent l'extrême fragilité des bancs résiduels bretons et insistent sur le fait qu'aucune exploitation durable de cette espèce ne pourra être menée sans une gestion très précise des populations résiduelles incluant conservation, restauration et suivis scientifiques. Pour les gestionnaires de l'environnement, ce rapport est l'occasion de mettre en lumière cette espèce-ingénieur, qui après trois siècles de surexploitation, est menacée de disparition. Pourtant une huitrière en bonne santé apporte de nombreux services écosystémiques, comme lutter contre l'érosion de la biodiversité et la dégradation de la qualité de l'eau. De nombreux éléments précis sont fournis pour permettre aux services de l'état, aux gestionnaires Natura 2000 et à l'OFB de protéger et restaurer les dernières populations présentes sur leurs périmètres d'intervention. En savoir plus sur le programme FOREVER et les autres projets européens de conservation et restauration de l'huitre plate : https://noraeurope.eu